﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Tensorflow
{
    public partial class RefVariable : VariableV1
    {
        public bool _in_graph_mode = true;
        public Tensor _initial_value;
        public string _graph_key;
        public bool _trainable;
        public Tensor _variable;
        public Tensor _snapshot;

        private Operation _initializer_op;
        public Operation initializer => _initializer_op;
        public Operation op => _variable.op;
        public Graph graph => _variable.Graph;
        public TF_DataType dtype => _variable.dtype;
        public TensorShape shape => tensor_util.to_shape(_variable.shape);

        public string name => _variable.name;

        public RefVariable(object initial_value,
            bool trainable = true,
            List<string> collections = null,
            bool validate_shape = true,
            string caching_device = "",
            string name = "",
            TF_DataType dtype = TF_DataType.DtInvalid) : 
            base(initial_value, trainable, collections, validate_shape, caching_device, name, dtype)
        {
            _in_graph_mode = true;

            _init_from_args(initial_value, trainable, collections, validate_shape, caching_device, name, dtype);
        }

        private void _init_from_args(object initial_value,
            bool trainable = true,
            List<string> collections = null,
            bool validate_shape = true,
            string caching_device = "",
            string name = "",
            TF_DataType dtype = TF_DataType.DtInvalid)
        {
            if (initial_value is null)
                throw new ValueError("initial_value must be specified.");

            var init_from_fn = false;

            if(collections == null)
            {
                collections = new List<string> { ops.GraphKeys.GLOBAL_VARIABLES };
            }

            // Store the graph key so optimizers know how to only retrieve variables from
            // this graph.
            _graph_key = ops.get_default_graph()._graph_key;

            _trainable = trainable;
            if (!collections.Contains(ops.GraphKeys.TRAINABLE_VARIABLES))
                collections.Add(ops.GraphKeys.TRAINABLE_VARIABLES);

            ops.init_scope();
            var values = init_from_fn ? new List<object>() : new List<object> { initial_value };
            Python.with<ops.name_scope>(new ops.name_scope(name, "Variable", values), scope =>
            {
                if (init_from_fn)
                {

                }
                // Or get the initial value from a Tensor or Python object.
                else
                {
                    _initial_value = ops.convert_to_tensor(initial_value, name: "initial_value");

                    var shape = _initial_value.shape;
                    dtype = _initial_value.dtype;
                    _variable = gen_state_ops.variable_v2(shape, dtype.as_base_dtype(), name);
                }

                // Manually overrides the variable's shape with the initial value's.
                if (validate_shape)
                {
                    var initial_value_shape = _initial_value.shape;
                }

                // If 'initial_value' makes use of other variables, make sure we don't
                // have an issue if these other variables aren't initialized first by
                // using their initialized_value() method.
                var _initial_value2 = _try_guard_against_uninitialized_dependencies(_initial_value);

                _initializer_op = gen_state_ops.assign(_variable, _initial_value2, validate_shape).op;

                if (!String.IsNullOrEmpty(caching_device))
                {

                }
                else
                {
                    ops.colocate_with(_initializer_op);

                    _snapshot = gen_array_ops.identity(_variable, name = "read");
                }

                ops.add_to_collections(collections, this);
            });
        }

        public Tensor _ref()
        {
            return _variable;
        }

        public Tensor _AsTensor()
        {
            return _snapshot;
        }

        /// <summary>
        /// Attempt to guard against dependencies on uninitialized variables.
        /// </summary>
        /// <param name="initial_value"></param>
        private Tensor _try_guard_against_uninitialized_dependencies(Tensor initial_value)
        {
            return _safe_initial_value_from_tensor(initial_value, new Dictionary<string, Operation>());
        }

        /// <summary>
        /// Replace dependencies on variables with their initialized values.
        /// </summary>
        /// <param name="tensor">A `Tensor`. The tensor to replace.</param>
        /// <param name="op_cache">A dict mapping operation names to `Operation`s.</param>
        /// <returns>A `Tensor` compatible with `tensor`.</returns>
        private Tensor _safe_initial_value_from_tensor(Tensor tensor, Dictionary<string, Operation> op_cache)
        {
            var op = tensor.op;
            var new_op = op_cache.ContainsKey(op.Name) ? op_cache[op.Name] : null;
            if(new_op == null)
            {
                new_op = _safe_initial_value_from_op(op, op_cache);
                op_cache[op.Name] = new_op;
            }
            return new_op.outputs[tensor.value_index];
        }

        private Operation _safe_initial_value_from_op(Operation op, Dictionary<string, Operation> op_cache)
        {
            var op_type = op.node_def.Op;
            switch (op_type)
            {
                case "IsVariableInitialized":
                case "VarIsInitializedOp":
                case "ReadVariableOp":
                    return op;
                case "Variable":
                case "VariableV2":
                case "VarHandleOp":
                    break;
            }

            // Recursively build initializer expressions for inputs.
            return op;
        }

        public override string ToString()
        {
            return $"tf.Variable '{name}' shape={shape} dtype={dtype}";
        }
    }
}
